Oh, I don't think, it really needs the plug. It's been around since forever, a proper GNU project and all that.
Sure enough, it's kind of niche, but there's even music archival projects that have been typesetting all the works of Mozart et al in Lilypond, so there's enough of a community to keep this ball rolling for the foreseeable future.

And well, that's also kind of where it's strongest: Transcribing existing music.
It's actually less well suited for composing, because you basically can only listen to things by generating a MIDI, and also you can't move measures around as easily.
But yeah, I still like it for composing, because I can use a text editor and Git and such, and personally, I also find it helpful to refer to notes with their names for figuring out intervals, rather than them just being random dots between lines...